Although formalin is commonly used a s a chemotherapeutant in fish culture, ill health conditions in some fish species a t therapeutic levels have been reported. The present study was conducted to investigate the effects of short term formalin bath treatments on the health status of fingerlings and sub-adults of Oreochromis niloticus, a culturable food fish in Sri Lanka. Health status of the fish was assessed in comparison to the control fish by monitoring survival, respiratory rates, erythrocytic indices in blood and histology of gill and liver tissues after one hour exposure to different concentrations of formalin followed by transfer to clean water for 7 days. No significant alterations with respect to the parameters studied were observed in the fingerlings exposed to 50 mg L-I formalin. Upon transfer to freshwater, formalin induced alterations in oxygen consumption rates and erythrocytic indices in the blood returned to normal levels after 7 days and histopathological changes in gill and liver tissues were observed to be restored to some degree. Results revealed that formalin could be used a t the level of 50 mg L-I for 1 hour for therapeutic purposes without undue harm to 0. niloticus fingerlings but special caution should be taken when high concentrations of formalin are used in culturing this species.

(frigate tuna), is a commercially fortunate to have a large resource of tuna, little information is available on the biology, genetics and stock structure of. Hence, the present study was conducted to study the biology, genetics and stock structure of in coastal October 2015 to September 2017 from day-boats operating in of Sri Lanka. For this period, the length-weight relationship and Fulton's condition factor (K) calculated for using standard length measured in centimetres and weight measured in grams were shown as = 0.1091 3.3385 and 1.93, respectively, indicating a relatively healthy growth pattern and a comparatively unpolluted habitat. Studies on the stomach contents revealed that are non-selective carnivors, shrimps and cephalopods available in the surrounding waters. The fecundity of female was shown to be 48,056 to 267,000 eggs. The calculated GSI values showed that the peak spawning period for male extends from May to August and for the females from May to July. The phylogenetic analysis of the mitochondrial D-loop region sequences of 75 selected samples representing all the geographical regions found in the coastal waters of the Western, North be considered as a single stock.

The artisanal, stake net fishery for shrimp in the Negombo lagoon, Sri Lanka, was studied over 2 years. There are around 22 sites, at which 57–63 stake nets can be fixed, at sites close to the sea mouth of the Negombo lagoon. The estimated mean catch rates of the fishery were 23.21 and 26.19 kg per operation in 1998 and 1999, respectively. The estimated annual fish productivity from the fishery reduced from 240 t in 1998 to 215 t in 1999. Subadults of penaeid shrimps formed 82% of the stake net catch. The net monthly income per fishermen varied from Rs. 5000 to 33 200 (mean = 13 667). In the Negombo lagoon stake net fishery, a mechanism for equity sharing was formulated by the fishing community.

Summary The length–frequency and age distributions, condition factor (K), gonadosomatic index (GSI) and gastrosomatic index (GaSI) of yellow catfish (Peltobagrus fluvidraco) were studied at three sites along the 500‐km longitudinal profile of Three Gorges Reservoir. Across all three sites (dam, mid‐reservoir and upper reservoir), GSI increased from April through June, with peak values observed in May and June. Mean K and GSI for fish captured near the dam were significantly higher compared to mid‐reservoir or upper‐reservoir areas. The GaSI index showed no significant variations across sites. However, the length‐frequency histogram of yellow catfish in the more riverine upper reservoir was log‐normal and skewed towards larger (total length) fish, a pattern that was significantly different from mid‐reservoir or near‐dam habitats, where fish length data were normally distributed but at a smaller length mode. Age estimations using otolith sagittae revealed that the spawning population was dominated by fish from only two age‐classes (1 and 2). This study provides novel insight into population characteristics of fish along the substantial spatial scale of Three Gorges Reservoir. Given the irregular population size‐ and age‐structure and the fact that the species is currently commercially exploited, this population is believed to be susceptible to overfishing. Restricted harvesting during peak reproductive months is recommended and suggested that additional research is needed on recruitment and harvest dynamics of this species throughout Three Gorges Reservoir. Additional research is also required to determine whether the spike in K and GSI at lentic sites is a transient product of recent impoundment or an indicator of optimal hydrologic habitat for the species.